Ink jet printers have printheads that operate a plurality of inkjets that eject liquid ink onto an image receiving surface. The ink can be stored in reservoirs positioned within the printer. Such ink can be aqueous, oil, solvent-based, or UV curable ink or an ink emulsion. Other inkjet printers receive ink in a solid form and then melt the solid ink to generate liquid ink for ejection onto the image receiving surface. In these solid ink printers, the solid ink can be in the form of pellets, ink sticks, granules or other shapes. Typically, an ink loader delivers solid ink pellets or ink sticks placed in the ink loader through a feed chute or channel to a melting device. A reservoir receives the melted ink and supplies the melted ink to one or more printheads. Other inkjet printers use gel ink. Gel inks are also heated to a predetermined temperature to alter the viscosity of the ink so the ink is suitable for ejection by a printhead.
A typical full width inkjet printer uses one or more printheads. Each printhead typically contains an array of individual nozzles for ejecting drops of ink across an open gap to an image receiving surface to form an image. The image receiving surface can be the surface of a continuous web of recording media, the surfaces of a series of media sheets, or the surface of an image receiving member, such as a rotating print drum or endless belt. Images printed on a rotating surface are later transferred and fixed to recording media by mechanical force in a transfix nip formed by the rotating surface and a transfix roller.
In an inkjet printhead, individual piezoelectric, thermal, or acoustic actuators generate mechanical forces that eject ink from an ink filled pressure chamber and through an orifice in response to an electrical voltage signal, sometimes called a firing signal. The amplitude, frequency, or duration of the firing signals affects the amount of ink ejected in each drop. The firing signal is generated by a printhead controller in accordance with image data. An inkjet printer forms a printed image in accordance with the image data by printing a pattern of individual ink drops at particular locations on the image receiving member. The locations where the ink drops land are sometimes called “ink drop locations,” “ink drop positions,” or “pixels.” Thus, a printing operation can be viewed as the placement of ink drops on an image receiving member in accordance with image data.
When printing on a continuous web or recording media, a spreading device is typically used to spread and fix the ink drops once they are placed on the media. The spreading device can include a high-load pressure roller configured with a conformable covering and an adjacent image side roller configured with a solid, non-conformable surface that interact to form a high-force nip into which the media is fed. The spreading and fixing of the ink on the media enables the printing operation to achieve a desired image quality and permanence. Occasionally, a wrinkle can form in the media web if the high-load pressure roller is out of alignment with the image side roller, or if the loading of the nip is not appropriate for the media weight, width or edge-registration position. In existing inkjet printers, an operator periodically inspects the condition of the web to visually detect whether a wrinkle is present. Once a wrinkle is detected, the operator implements a maintenance procedure to eliminate the wrinkle. Consequently, the operator may not detect the wrinkle until its severity passes an unacceptable threshold. Moreover, even after the wrinkle is detected, the operator must further determine if the wrinkle is inboard or outboard of the center of the web so that the pressure roller can be adjusted accordingly. Therefore, automated detection of the presence and position of a wrinkle in moving web is desirable to minimize machine downtime and material waste arising from continued printing while a wrinkle condition exists.